The transport of particulate material from a relatively low pressure zone to a relatively high pressure zone is usually done by means of a lock hopper system. By opening a first valve, the material is transferred from a storage vessel to a lock hopper. The valve is closed and the lock hopper is brought to an elevated gas pressure. A second valve, connecting the lock hopper to a vessel at elevated pressure, is then opened and the material is fed into this latter vessel and from there to the elevated pressure zone. The second valve is then closed and the gas pressure in the lock hopper is reduced. Opening the first valve marks the beginning of a new cycle.
This process is discontinuous. Moreover, the valves connecting the vessels become badly worn by the abrasive effect of the material, in combination with the frequent opening and closing. Regular replacement of these valves becomes necessary. The invention seeks to overcome these problems.